a theory I have, not sure if it works
Could oz be the baby that lived from the first season. They never really say that one of the mothers is actual biological mother, could be adopted right? I dont remember season one too good. I figured some diehard fans with better memories might know. They are liking to tie the seasons together today. This would be mouth dropping if done correctly.
I feel like he killed someone at end of first season. Was he young enough to forget that he did that if he is now oz? Maybe babysitter showing him videos wakes up his true self.
All silly thinking, just a thought I had